The present invention relates to the field of heating, ventilating and air-conditioning and more particularly to the area of temperature controls.
Thermostats have in more recent times have been constructed in two major components: a housing and a sub-base. Prior art FIG. 1 provides an example. The thermostat 200 included a housing 201 and a sub-base 202. The housing usually contained a temperature sensor (not shown), a display 215 and some form of a setpoint selection means, here shown as keys 206 through 211. The display and setpoint selection means were sometimes jointly referred to as the user interface. The sub-base included typically included wiring terminals to connect the thermostat to an HVAC plant. The HVAC plant may include any or all of the following: heat pump, air-conditioner, furnace (either fossil fuel or electric), boiler and fan.
An advance in the thermostat field occurred when a controller was used for control functions within a thermostat such as the thermostat described in U.S. Pat. No. 4,606,401 (Levine) issued Aug. 19, 1986 and commonly assigned with the present invention. The controller acted on preprogrammed instructions and stored, user entered parameters to control a temperature within a space to a desired setpoint at a given time. The controller generally used was a microprocessor. Setpoints were associated with time periods throughout the day. When the time crossed a time period boundary, a new setpoint was used (which may be the same temperature as the previous setpoint).
In order to increase the temperature of a space controlled by such a thermostat, especially at the boundaries of time periods, adaptive recovery processes were developed. In FIG. 2, a prior art time versus temperature graph is shown. SP1 indicates the setpoint of the thermostat between times t0 and t1 and SP2 indicates the setpoint after time t1. In order to have the actual temperature (represented by continuous points AT) reach SP2 at or before time t1, a ramp begins at time t2. Once the AT crosses the ramp, the setpoint snaps to SP2.
Usually, a thermostat was configured to operate only with one type of HVAC plant at a time. For example, because of the differing control requirements for a heat pump, an electric furnace and a fossil fuel furnace and an air conditioning system, a thermostat was set up to handle only one of these types of HVAC plant. In particular, different adaptive recovery processes were required for heat pumps and furnaces. This led to different thermostats being required for each.